Power consumption limit associated with power over ethernet (POE) computing system

ABSTRACT

A computing system is associated with power consumption based on Power over Ethernet (PoE). Power consumption is compared to a threshold, and a signal is asserted that power consumption is to be limited based on the comparison to the threshold.

PRIORITY APPLICATION INFORMATION

This application is a continuation of U.S. National Stage Entryapplication Ser. No. 14/232,918 filed on Jan. 15, 2014, which claimspriority to International Application No. PCT/US2011/044317 filed onJul. 18, 2011. The contents of which are incorporated herein byreference in its entirety.

BACKGROUND

Networks, such as local area networks (LANs) and wide area networks(WANs), may distribute network data and power over the network usingPower over Ethernet (PoE). PoE is specified in the Institute ofElectrical and Electronics Engineers (IEEE) Standard 802.3 and otherrelevant standards, describing power delivery by a Power SourcingEquipment (PSE) to a Powered Device (PD). The standards limit powerdelivery by the PSE to a power delivery envelope.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a block diagram of an architecture of a computing systemincluding a power converter according to an example.

FIG. 2 is a block diagram of an architecture of a computing systemincluding a power converter according to an example.

FIG. 3 is a block diagram of a Power over Ethernet (PoE) systemincluding a power converter according to an example.

FIG. 4 is a circuit block diagram of a power converter according to anexample.

FIG. 5 is a graph of power consumption and a power high signal over timeaccording to an example.

FIG. 6 is a flow chart based on power consumption of a computing systemaccording to an example.

FIG. 7 is a flow chart based on power consumption of a computing systemaccording to an example.

The present examples will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements.

DETAILED DESCRIPTION

A Powered Device (PD), such as a computing system including anAll-in-One (AiO) zero client, may draw power from a Power SourcingEquipment (PSE) via Power over Ethernet (PoE). The PSE may impose apower budget that can constrain design choices of PDs, and powerconsumed by the PD may fluctuate over time, based on factors such asusage scenarios of the PD. A PSE may shut down power to a PD, inresponse to the PD attempting to draw power in excess of the availablepower envelope. Thus, design choices of PDs may be further constrainedin view of power limitations to avoid shutdowns while accommodatingvariations in usage scenarios of the PDs and the accompanyingpower/usage scenarios. Accordingly, the PD may provide enhancedfunctionality by monitoring its own power consumption relative to athreshold associated with the power budget, and asserting a signal tolimit its power consumption accordingly. Power consumption may bedynamically monitored and limited selectively, such as by reducingbrightness of a display when total power consumption reaches and/orexceeds the threshold. Thus, the PD enables enhanced functionality,while dynamically complying with power budgets and avoiding being shutdown by the PSE for exceeding the power budget.

FIG. 1 is a block diagram of an architecture of a computing system 100including a power converter 150 according to an example. Computingsystem 100 also includes power meter 140 and component 132. Computingsystem 100 may receive power at power converter 150 via Power overEthernet (PoE) 152, which may be provided by a Power Sourcing Equipment(PSE) such as a switch and/or midspan (not shown in FIG. 1).

Power converter 150 may provide converted power to computing system 100,including component 132. Power meter 140 may monitor power consumptionof the computing system 100, and compare the power consumption tothreshold 132. For example, power meter 140 may determine powerconsumption based on output of power converter 150, and threshold 132may correspond to a specified level of power output from power converter150. Threshold 132 may be based on a PoE power class associated withcomputing system 100. For example, threshold 132 may correspond to anupper power limit for a type 1 PoE Powered Device (PD) of class 3,having an upper power limit of 12.95 Watts at the PD.

Power meter 140 may assert a signal 160 that is sent to component 132 ofcomputing system 100. Signal 160 may indicate that power consumption isto be limited in view of power consumption compared to the threshold132. Component 132 may adjust its power consumption based on signal 160.For example, component 132 may be a display that dims its brightness inresponse to signal 160, to reduce overall power consumption of computingsystem 100.

FIG. 2 is a block diagram of an architecture of a computing system 200including a power converter 250 according to an example. Computingsystem 200 is connected to network 204 via switch 202. Switch 202 is aPower over Ethernet (PoE) Power Sourcing Equipment (PSE). Thus, switch202 may provide power to the computing system 200 via PoE 252. PoE mayalso be provided in conjunction with a midspan (not shown) to injectpower for PoE 252. Computing system 200 may include a system board 220,and may include a display 206.

Display 206 may be a Liquid Crystal Display (LCD) Module (LCM),including panel 208 and Back-Light Unit (BLU) 210. Display may include aback-light converter board (not specifically shown), such as a LightEmitting Diode (LED) driver for LED back-lighting.

System board 220 may include a processor 222, USB host 224, component232 (including a network card, Local Area Network (LAN)-On-Motherboard(LOM), or other component for a computing system), power meter 240, andpower converter 250. USB host 224 may be coupled to devices such askeyboard 226, mouse 228, and USB devices 230. Power converter 250 mayreceive power from switch 202 via PoE 252.

Power converter 250 is a PoE-powered device (PD) power converter. Powerconverter 250 provides power to computing system 200. For example, acomponent, such as BLU 210 or other components, may receive powerdirectly from power converter 250 via unmetered power 258. Powerconverter 250 may provide power via a first voltage rail 254 and asecond voltage rail 256. First voltage rail 254 and a second voltagerail 256 may be provided to power meter 240.

Power meter 240 may determine power consumption of computing system 200.For example, power meter 240 may determine power consumption based onfirst voltage rail 254 and/or second voltage rail 256. Power meter 240may determine power consumption based on PoE 252 or other sources fordetermining or deriving power consumption. Power meter 240 may include ashunt resistor to receive a voltage and measure a voltage drop acrossthe shunt resistor to calculate power associated with that voltage.

Power meter 240 may monitor power consumed on first voltage rail 254,and estimate power consumption of second voltage rail 256 to determinetotal power consumption of computing system 200. Power meter 240 maydistribute power to components of computing system 200. For example,power meter 240 may distribute power derived from the first voltage rail254 to processor 222, USB host 224, and component 232. Power meter 240may distribute power derived from the second voltage rail 256 to thedisplay 206 and/or the BLU 210. Power meter 240, and/or components ofcomputing system 200, also may further convert the first voltage rail254 and/or the second voltage rail 256 to provide additional voltages.

Power meter 240 may provide a signal 260 to components of computingsystem 200. For example, power meter 240 may determine that powerconsumption of computing system 200 has exceeded a threshold, and sendsignal 260 to display 206, processor 222, USB host 224, and/or component232. Signal 260 may indicate adjusting display 206 such that powerconsumption is reduced. BLU 210 may be instructed to dim the display 206to reduce power consumption. Accordingly, power meter 240 may monitorfirst voltage rail 254, and cause reduction of power in a component(such as display 206) deriving power from the second voltage rail 256.Thus, computing system 200 may enable control of power consumption ofcomponents independently of power consumption that is monitored,isolating and improving accuracy of the monitoring.

The monitored power consumption may be used to determine powerconsumption of the entire computing system 200. For example, thecomputing system 200 may monitor and determine a first power consumptionassociated with the first voltage rail 254. The computing system 200 mayalso identify predetermined level of power consumption associated withthe display 206 consuming power from the second voltage rail 256, basedon a level of power limiting applied to the display 206. For example,the computing system 200 may identify that the display 206 is driven at50% brightness associated with a known wattage. For a given display orother component, various levels of power consumption may be determinedbased on a correlation with various levels of power limiting. Thecomputing system 200 may further identify additional sources of powerconsumption, such as power conversion/transmission losses and otheroperational losses. Thus, total power consumption of computing system200 may be determined based on the monitored power consumption of thefirst rail, the estimated power consumption of the second rail, andadditional losses. The computing system may, therefore, respond to anincrease in monitored power consumption of the first rail byimplementing power savings to decreasing estimated power consumption ofthe second rail.

Power meter 240 may signal various components so that computing system200 operates in compliance with a power budget associated with PoE andthe PSE. An example power budget may be based on available power of 13watts. Power converter 250 may be associated with a conversionefficiency, such as 91%, resulting in approximately 11.83 watts ofconverted power available after power conversion. The computing system200 may use this available power as follows, according to one example:system board 220, including keyboard 226 and mouse 228, may use 4.5watts. Input/Output (I/O), via two USB devices 230 using 100 milliampseach up to a maximum of 500 milliamps each, may use 1 watt. A displaydriver hardware such as a scalar (not shown) associated with panel 208,may use 1.5 watts. The BLU 210 may use 0.24 watts+2.77 watts=3.01 watts.Panel 208 may use 1.8 watts. Thus, total power usage budget of examplecomputing system 200 may be 4.5+1+1.5+3.01+1.8=11.81 watts,approximately, falling below the available PoE converted power budget of11.83 watts.

Power savings can be realized in using efficient structures, whilesupporting a large screen (e.g., approximately 18.5 inches diagonal).High efficiency white light emitting diode (WLED) back lighting, emittedfrom an assembly of WLEDs for example, may be directed into a lightguide/BLU to provide sufficient lighting while being powered byapproximately 2.77 watts or less (depending on advancements in lightingtechnology). Thus, a LCM using such a BLU may consume 4.57 watts orless. The BLU may be associated with a top diffuser, back reflector,bottom diffuser, and prism. A contrast ratio may also be reduced to savepower, while providing brightness of 200 nits (candelas per squaremeter) or greater using the BLU.

FIG. 3 is a block diagram of a Power over Ethernet (PoE) system 300including a power converter 350 according to an example. System 300further includes switch 302, network jack 360, Ethernet magnetics 362,and network physical layer (PHY) chip 364. System 300 may include amidspan (not shown) associated with switch 302 to inject power into PoE352. For example, a non-PoE switch 302 may be used to provide networkdata, and a midspan may be used to provide PoE power.

Switch 302 is a PSE-switch, capable of providing power sourcing topowered devices interfacing with the switch 302. Switch 302 may providepower using PoE 352. PoE 352 includes an Ethernet signal and power,illustrated as 48 volts. Network jack 360, illustrated as registeredjack 45 (RJ45), may interface with switch 302 to send/receive PoE 352.RJ45 may include eight pins to carry signals, including power andEthernet, simultaneously.

PoE 352 is received at Ethernet magnetics 362, where power 366 isseparated from Ethernet 368. Ethernet 368 may be sent to the PHY chip364, and power 366 may be sent to the power converter 350. Asillustrated, the power sourcing equipment (PSE) switch 302 may provide13 Watts of power, including providing power at 48 volts. The PSE mayprovide up to 15.4 Watts according to PoE specifications, such that apowered device (PD) is guaranteed 13 Watts at the PD. PoE specificationsallow for 2.4 Watts to be lost in cable/transmission. The illustratedvalues of 13 Watts and 48 Volts are associated with type 1 PoE, andrepresent values with valid ranges and may vary depending on specificimplementations/types/classes.

Power converter 350 may convert the power 366 from Ethernet magnetics362 to various voltage levels, such as 3.3 volts, 5 volts, 12 volts, 30volts, 48 volts, and others, including voltages based on needs of chips,power rails, and other components of the computing system. Converter 350may be associated with an efficiency, such as approximately 91%,providing approximately 11.8 W from the available 13 W from Ethernetmagnetics 362. Power converter 350 may provide first voltage rail 354and second voltage rail 356, which may carry separate, independentvoltage levels. Additional voltage rails are possible, and voltage railsmay be enhanced by further conversion, dividing, and/or boosting.

Power from PoE may be provided by PSE switch 302 to a powered device(computing system) based on a power class associated with the computingsystem. The power class may be associated with a standard, such as IEEE802.3-2008 (full spec) & IEEE 802.3 AT-2009 (addendum), specifyingclasses of power between a PSE and a powered device (PD) drawing powerfrom the PSE via PoE. The class may be associated with a type of PoEPSE, such as a type 1 PSE device and a type 2 PSE device. The computingsystem PD may be a type 1 device compatible with type 1 or type 2 PSEdevices. Compliance with type 1 enables benefits by more readily takingadvantage of available infrastructure. Additional benefits include costsavings due to lower power requirements.

A powered device may make its readiness known to the PSE, and indicateits PoE class, by presenting specified resistance values to interfaceswith the PSE. A powered device may draw power according to the class,and the PSE may terminate power delivery if the powered device drawsexcessive power for the power class requested by the device. Thus, theavailable power provided by PoE is not unlimited. For an example class,a device may draw approximately 13 watts at 48 volts, which correspondsto drawing approximately 270 milliamps of current. Actual values mayvary from nominal values listed in the specification, and example PDsmay monitor power, current, and/or voltage for determining actual values(e.g., monitoring actual power and current to derive actual voltage).Thus, it is beneficial to use the available power for a power class ofpowered devices, without running afoul of the power limitationsassociated with the class that may result in the PSE removing powercausing shutdown of the powered device.

Examples herein may request available power for a power class, and becapable of dynamically using that power to its fullest while allowingfor variations in usage scenarios of the computing system/powereddevice. The variations in usage scenarios can affect power drawn fromthe PSE according to the power class, including drawing additional powerbeyond the power class but within tolerances of the power classaccording to PoE specifications. For example, PoE standards may permit apowered device to draw limited current peaks that increase theinstantaneous power above the nominal limits, in view of the averagepower requirements. Power usage by the powered device is enhanced for agiven power class budget, without resorting to renegotiating orotherwise switching to a different power class. Furthermore, a PSE maybe specified to provide power at a greater limit than power specified tobe drawn by a powered device. For example, a PSE may be specified todeliver 15.4 watts, compared to the specification for a powered devicespecifying drawing only 12.95 watts (e.g., accounting for power lossesdue to interface connections/cable loss between the PSE and the PD).

FIG. 4 is a circuit block diagram of a power converter 400 according toan example. Power converter 400 includes a primary side 402 and asecondary side 404. The primary side 402 is associated with input fromPoE 452. For example, power converter 400 may receive 48 volt inputs onfour lines of PoE 452, labeled as P12, P36, P45, and P78. The four linesmay correspond to signals output from PoE magnetics (e.g., Ethernetmagnetics 362, see FIG. 3), which strip off a Direct Current (DC)voltage from the Ethernet transmit (TX) and receive (RX) pairs. Outputmay be received from standard interconnection pins of an Ethernetplug/jack carrying PoE 452. VDD and VSS may be derived from PoE 452,using a network of diodes as illustrated (including a diode bridge), forexample. VSS may be applied to converter processor 422. VDD may beapplied to an inductor, a first transformer winding 426, and transistor424. Transistor 424 may open and close according to input from converterprocessor 422. Converter processor 422 also may interface with secondtransformer winding 428 via a diode. In the illustrated example,converter processor 422 is a Texas Instruments TPS23757 chip, a HighEfficiency PoE Interface and DC/DC Controller. Other chip(s) and/orcircuitry may be used to provide the primary side 402, and to provideand interface with the secondary side 404. One transformer may be usedto provide first transformer winding 426 and second transformer winding428, which may be located around the same transformer core.

Secondary side 404 is associated with providing first voltage rail 454and second voltage rail 456. Values of 5 V and 12 V are shown, althoughother voltage values are possible in alternate examples. First voltagerail 454 receives power via first transformer winding 426. Secondvoltage rail 456 receives power via second transformer winding 428.First transformer winding 426 interfaces with first driver 430, andsecond transformer winding 428 interfaces with second driver 432. Firstdriver 430 and second driver 432 may operate synchronously with theturning on and off of the transistor 424 to operate the firsttransformer winding 426 and second transformer winding 428. Circuitrymay operate as a flyback converter.

Secondary side 404 is also associated with power meter 440, system 420,brightness control 412, back-light driver 414, booster 416, andback-light unit 410. First voltage rail 454 may be provided to powermeter 440, which can determine power consumption of system 420, whichmay include power consumption of back-light unit 410 and other units.Power meter 440 may assert signal 460 to brightness control 412,indicating a high-power state of the computing system 420 such thatpower is to be limited. Brightness control 412 may provide a signal toback-light driver 414, such as a Pulse-Width Modulated (PWM) signalindicating a duty cycle, wherein the duty cycle may be reduced accordingto signal 460 to reduce brightness. Back-light driver 414 may receivepower from booster 416, which may derive a boosted signal from secondvoltage rail 456. For example, a boosted voltage of 30 Volts may beprovided to back-light driver 414. Thus, back-light driver 414 may drivethe back-light unit 410 to provide controlled brightness based on thefirst voltage rail 454, signal 460, and the second voltage rail 456.

FIG. 5 is a graph of power consumption 500 and a power high signal 560over time according to an example. Power consumption 500 may vary overtime, depending on operations performed and components powered accordingto various usage scenarios. A computing system according to examplesherein may have the capability of utilizing a power envelope associatedwith the computing system, without risking being shut-down by a PSEproviding PoE to the computing system.

Power consumption 500 may include a first power consumption 501 based onconsumed power associated with a first voltage rail, and a combinedpower consumption 502 based on consumed power associated with both thefirst voltage rail and the second voltage rail. First power consumption501 may be monitored regarding first threshold 503 and second threshold504. Based on first power consumption 501, a computing system maycontrol a component using the second voltage rail, to affect combinedpower consumption 502.

Accordingly, combined power consumption 502, including power consumptionbased on the first voltage rail and the second voltage rail, may avoidexceeding PoE Threshold 505. A computing system also may be associatedwith additional power consumption (not shown in FIG. 5), such as lossesdue to transmission and conversion of power, generation of heat, variouscomponents, and other losses. Such additional power consumption may beaccounted for in association with first threshold 503, second threshold504, and PoE threshold 505, to avoid exceeding the PoE threshold 505. Atotal power consumption of the computing system may be affected byvarious types of power consumption that may be factored into usagescenarios.

First power consumption 501 may represent an example usage scenario suchas insertion, initialization, and access of a Universal Serial Bus(USB)-powered hard drive storage device, that consumes power from thefirst voltage rail. First power consumption 501 rises initially uponinserting the USB device, continuing to rise as the USB device's harddrive consumes power to spin up and initialize. First power consumption501 levels off and falls to a steady state as the hard drive finishesinitializing and is accessed to read/write data then transition into anidle state. Other usage scenarios and power consumption patterns arepossible, depending on the type and combination of components anddevices used, including what voltage rail is used. Other usage scenariosinclude the computing system decoding and displaying aprocessor-intensive audio/video stream displaying alternating colors andcontrast at full brightness. Power consumption may fluctuate accordingto instantaneous blips of activity or sustained usage. Displaying avisual pattern on screen may affect power draw dynamically, such asdisplaying full-screen alternating black-and-white pixels.

Combined power consumption 502 may include first power consumption 501corresponding to the first voltage rail, and additional powerconsumption corresponding to the second voltage rail. Combined powerconsumption 502 may be vertically offset from first power consumption501 corresponding to additional power consumption of the second voltagerail, for example by back-light usage. Thus, dimming the backlight mayreduce power consumption of the second voltage rail, and accordingly mayreduce the vertical offset separating the first power consumption 501and the combined power consumption 502. Combined power consumption 502may represent an approximation, that may ignore various incidental powerconsumption and other losses. Reducing combined power consumption 502,and correspondingly reducing total computing system power consumption,enables power consumption 500 to remain within a PoE threshold 505 toavoid power shut down by the PSE.

At time t1 506, first power consumption 501 reaches first threshold 503,which triggers assertion 562 of power high signal 560. Signal 560 may beasserted 562 when first power consumption 501 is within a power range ortime range (minimum assertion width) of first threshold 503, includingwhen below first threshold 503. Assertion 562 of power high signal 560may indicate that power saving measures may be appropriate. For example,a power meter may assert the power high signal 560 to instruct aback-light unit to reduce power consumption and dim the backlight.Accordingly, also at time t1 506, combined power consumption 502 isshown decreasing by an amount of power saved by dimming the backlight.In the illustrated example, the combined power consumption 502 includesone incremental decrease corresponding to one incremental dimming of theback-light. In alternate examples, the back-light may be dimmed based onmany increments, such that combined power consumption 502 may be reducedbased on many incremental steps. Other components of a computing system,such as a processor, may include incremental power savings. Assertion562 of power high signal 560 may include an indication of theincremental amount that power savings are to be implemented for acomponent.

Assertion 562 of power high signal 560 may indicate various amounts bywhich to reduce power consumption 500. For example, an amount by whichpower is to be reduced may be associated with the extent to which firstpower consumption 501 may exceed first threshold 503.

In the example usage scenario after time t1 506, first power consumption501 drops below first threshold 503 and continues toward secondthreshold 504. Power high signal 560 remains asserted 562 after firstpower consumption 501 drops below first threshold 503. Thus, hysteresisis involved with assertion 562 and de-assertion 564 of the power highsignal 560, because different thresholds may be involved with changes ofstate in power high signal 560, and previous state(s) of the power highsignal 560 may be involved in changes to its current and/or futurestate(s). For example, the power high signal 560 may be asserted 562 atthe first threshold 503 if the power high signal 560 was previously in astate of de-assertion 564. The power high signal 560 may be de-assertedat the second threshold 504, if the power high signal 560 was previouslyin a state of assertion 562. The de-assertion 564 also may depend ondelay 512.

Delay 512 enables power high signal 560 to remain asserted 562 afterfirst power consumption 501 drops below second threshold 504. Thus, evenwhen first power consumption 501 drops rapidly and passes below firstthreshold 503 and second threshold 504 as shown, de-assertion 564 may bedelayed to guarantee a minimum amount of time that power high signal 560remains asserted 562. Thus, a computing system may control transitionsbetween assertion 562 and de-assertion 564, independently of power loadsand situations where the computing system quickly returns to a low powerstate. Such control may avoid distraction that would be caused if thescreen were to dim and brighten in rapid succession, based on powerconsumption changes alone. Thus, examples may avoid visual “chatter”where a display flickers or pulses between dimmed and non-dimmed modes.Use of independent power sources (e.g., independent first and secondvoltage rails) may also help prevent chatter, by enabling monitoring offirst power consumption 501, whose power consumption is independent ofadjustments made to power consumption of the second voltage rail.

At time t3 510, the power high signal 560 is de-asserted 564. T3 510 maybe calculated based on time t2 508 and delay 512. After time t3 510, thepower high signal 560 may remain de-asserted 564 until power consumptionreaches the vicinity of first threshold 503. Thus, the example powerconsumption 500 envelope shown in FIG. 5 allows for a large range ofpower consumption scenarios, without visual chatter or other drawbacksthat potentially may be associated with operating under reduced powerconsumption.

FIG. 6 is a flow chart 600 based on power consumption of a computingsystem according to an example. Step 610 includes monitoring powerconsumption of a computing system that is to draw power from Power overEthernet (PoE), wherein the monitoring is performed locally by thecomputing system. The monitoring may be based on power drawn from thePoE, power consumed by a power converter, power consumed by componentsreceiving various voltage outputs from the power converter, and/oralternate techniques of monitoring power consumption including derivingpower consumption of a first component based on power consumption of asecond component. Step 620 includes comparing the power consumption to afirst threshold associated with a PoE power class associated with thecomputing system, wherein the comparing is performed locally by thecomputing system. For example, the computing system can maximize use andfunctionality of available power while avoiding exceeding power envelopelimits of a PoE power class associated with the computing device. Thecomputing system may exceed a nominal power limit for a duration oftime, then reduce power consumption and avoid shutdown of the suppliedPoE. A computing system can benefit from an expanded power envelope,while avoiding remote shutdown of supplied power caused by exceeding thenominal power envelope. Step 630 includes asserting a signal to limitthe power consumption at the computing system based on the comparing,wherein the asserting is performed locally by the computing system.Thus, the computing system may control itself to avoid conflicting withpower envelope limits imposed remotely by the power sourcing equipment,providing benefits of a bottom-up approach to managed power consumptionfor powered devices interfacing with a PoE power source.

FIG. 7 is a flow chart 700 based on power consumption of a computingsystem according to an example. In step 710, the computing systemmonitors its power consumption. In step 720, the computing systemcompares power consumption to a first threshold. In the illustratedexample, the comparison tests whether power consumption is equal to orgreater than the first threshold. However, in alternate examples, thecomparison may test whether power consumption is within a range of thefirst threshold (based on a range of time or a range of amount, etc.).The comparison may be expressed as: “|P−Threshold1|≤Range1?” Thecomparison may also check a current and/or previous state of signalassertion. In an example, a first power consumption limitation maytrigger when a first power consumption is within a range of one watt tothe threshold, and a second power consumption limitation may triggerwhen first power consumption is equal to the threshold. Different rangesmay be used for different power consumptions, such as using a highertrigger threshold range for power consumptions that fluctuate widely.The comparison may also take into consideration a present/past powerconsumption level and its proximity to a threshold, when asserting asignal that power consumption changes are to be made. For example, thecomputing system may decrease power consumption more aggressively whenpower consumption is near a threshold. Power consumption may bedecreased based on a varying scale over time. For example, a back-lightduty cycle can be reduced successively by 10%, then by 20%, then by 50%over time if power consumption remains within a range of a thresholddespite earlier power consumption reduction signal assertions. Othervariations and combinations are possible in alternate examples.

If the comparison in step 720 is not satisfied, execution of the flowchart 700 returns to step 710. If the comparison in step 720 issatisfied, execution proceeds to step 730. In step 730, the computingsystem asserts a signal to limit power consumption. For example, thecomputing system may assert PoE_PWR_HIGH signal 460 illustrated in FIG.4. In step 740, the computing system adjusts operation of a componentbased on the signal, i.e., the signal asserted in step 730. For example,the computing system may adjust brightness and/or processor operation tolimit power consumption. The types of adjustments to limit powerconsumption may be indicated in or derived from the asserted signaland/or past/present power consumption and signal conditions/states.

In step 750, the computing system compares power consumption to a secondthreshold. In the illustrated example, the comparison tests whetherpower consumption is equal to or less than the second threshold.However, in alternate examples, the comparison may test whether powerconsumption is within a range of the second threshold. The comparisonmay be expressed as: “|P−Threshold2|≤Range2?”, for example. Thecomparison may also take into consideration current and previous powerconsumption and signal assertion states, and may be associated withadditional features set forth above, such as features associated withstep 720.

If the comparison in step 750 is not satisfied, execution of the flowchart 700 returns to step 730. If the comparison in step 750 issatisfied, execution proceeds to step 760. In step 760, the computingsystem determines if a time delay is expired, e.g., delay 512 shown inFIG. 5. If the time delay is not expired, execution returns to step 730.If the time delay is expired in step 760, execution proceeds to step770. In step 770, the computing system de-asserts the signal associatedwith limiting power consumption. Execution proceeds to step 710,completing a circuit of all steps of the feedback loop associated withmonitoring power consumption. Thus, a computing system may fully utilizea power envelope associated with a corresponding PoE power class.

The breadth and scope of the present invention should not be limited byany of the above-described examples, but should be defined in accordancewith the following claims and their equivalents.

What is claimed is:
 1. A system, comprising: a power converter to drawpower from Power over Ethernet (PoE) and power the system with an amountof PoE converted power; a display including a backlight, wherein:converted PoE power consumption of the display is limited based on asignal indicating that the total converted PoE power consumption of thesystem is to be limited; the display derives power from a second voltagerail; and the backlight to vary the brightness while maintaining athreshold level of brightness as converted PoE power provided via thesecond voltage rail to the backlight varies to limit the total convertedPoE power consumption; and a power meter to: compare an amount of PoEconverted power consumption on a first voltage rail to a thresholdamount of power consumption, wherein the first voltage rail is differentthan the second voltage rail; maintain assertion of the signal based ona determination that the amount of PoE converted power consumption isgreater than the threshold amount of power consumption; and de-assertthe signal based on a determination that the amount of PoE convertedpower consumption is less than the threshold amount of powerconsumption.
 2. The system of claim 1, further comprising the powermeter to: reduce an amount of PoE converted power to the second voltagerail; and maintain an amount of power to a processor in the system,wherein the processor derives power from the first voltage rail.
 3. Thesystem of claim 1, further comprising the power converter to: providepower comprising a first voltage; and provide power comprising a secondvoltage to power a component of the system.
 4. The system of claim 3,further comprising the power meter to compare power based on the firstvoltage.
 5. A power converter, comprising: an input to receive Powerover Ethernet (PoE) from a power source; a transformer to convert thePoE received from the power source to an amount of available PoEconverted power provided by a first voltage rail; and a power meter to:compare a total amount of PoE power consumption to a first threshold;assert a signal indicating that the total amount of converted PoE is tobe limited based on a determination that the total amount of PoE powerconsumption is above a first threshold; compare the total amount of PoEpower consumption to a second threshold; maintain assertion of thesignal based on a determination that the total amount of PoE powerconsumption is greater than the second threshold; de-assert the signalbased on a determination that the total amount of PoE power consumptionis less than the second threshold; and vary a brightness of a backlightof a display while maintaining a threshold level of brightness as anamount of PoE power provided via a second voltage rail to the backlightvaries.
 6. The power converter of claim 5, further comprising the powermeter to reduce the amount of PoE power to the second voltage rail,wherein the second voltage rail is different than the first voltagerail.
 7. The power converter of claim 5, further comprising the powermeter to maintain an amount of PoE to the first voltage rail, whereinthe first voltage rail provides power to a processer of a computingsystem.
 8. The power converter of claim 5, wherein the power meter is toassert the signal that power consumption is to be limited based on adetermination that the total amount of PoE power consumption is abovethe first threshold for a first period of time.
 9. The power converterof claim 5, wherein the power meter is to assert the signal that powerconsumption is to be limited based on a determination that the totalamount of PoE power consumption is above the first threshold by a firstamount.
 10. A method, comprising: monitoring, at a first voltage rail, atotal amount of converted Power over Ethernet (PoE) power consumption bya system; asserting a signal to limit the total amount of converted PoEpower consumption by the system based on a comparison of the totalamount of converted PoE power consumption by the system to a firstthreshold amount of converted PoE power consumption; limiting theconverted PoE power consumption of a component of the system, whereinthe component is powered by a second voltage rail that is different thanthe first voltage rail, and wherein the system includes a displayincluding a backlight to vary in brightness while maintaining athreshold level of brightness as converted PoE power provided via thesecond voltage rail to the backlight varies; comparing the totalconverted PoE power consumption of the system to a second threshold;maintaining assertion of the signal based on a determination that thetotal converted PoE power consumption is greater than the secondthreshold; and de-asserting the signal based on a determination that thetotal converted PoE power consumption is less than the second threshold.11. The method of claim 10, wherein limiting the converted PoE powerconsumption of a component of the system includes: limiting an amount ofpower to the second voltage rail; and maintaining an amount of power tothe first voltage rail.
 12. The method of claim 10, wherein limiting theconverted PoE power consumption of a component of a system includesmaintaining an amount of power to a processor of the system.
 13. Themethod of claim 10, further comprising: monitoring power consumptionbased on a first voltage output of a PoE power converter; and adjustingpower consumption of a plurality of components of the system associatedwith a second voltage output of the PoE power converter.
 14. The methodof claim 10, further comprising asserting a signal to reduce power tothe component by a variable amount based on a difference between theamount of PoE power consumption and the first threshold.